1. Field of the Invention
The invention relates to a process for the production of 2-(methylthio)-disodium barbiturate of the formula: ##STR1## starting from thiourea, malonic acid dimethyl ester and sodium methanolate.
2. Background Art
2-(Methylthio)-disodium barbiturate is an important intermediate product for the production of the herbicide difluoromethyl thiobarbiturate (U.S. Pat. No. 4,692,524).
The production of monosodium thiobarbiturate starting from malonic acid dimethyl ester, thiourea and sodium methanolate is known. These three initial materials are used in an approximately molar ratio of 1:1:1 (European Published Patent Application No. 411,277). In addition the next stage, that is, the methylation of this monosodium thiobarbiturate with methyl bromide to 2-(methylthio)-barbituric acid, is known and this reaction is performed under increased pressure (European Published Patent Application No. 411,276).
A drawback of this two-stage synthesis for the production of 2-(methylthio)-barbituric acid is that in the first stage the monosodium thiobarbiturate is formed, and then, in the next stage, the latter reacts only under increased pressure and higher temperature with methyl bromide to 2-(methylthio)-barbituric acid. A further drawback is that 2-(methylthio)-barbituric acid cannot be converted directly into difluoromethyl thiobarbituric acid but only by an intermediate stage.